Degradable hydrazone curing agents and applications thereof

ABSTRACT

This invention provides, among others, curing agents of Formulae (I) and (II), methods for preparing these curing agents, prepreg materials, degradable cross-linked polymers and reinforced composites made from these curing agents and epoxy resins, and methods for degrading and/or recycling the degradable polymers and reinforced composites.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and benefit of Chinese PatentApplication No. 201310440092.0, filed on Sep. 24, 2013, the contents ofwhich are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This application is in general in the field of epoxy curing agents andapplications thereof, and more specifically relates to degradable cyclicacetal, cyclic ketal diamines epoxy curing agents; prepreg materials,polymers, or reinforcing composite materials based thereon; anddegradation of the polymers and reinforced composite materials basedthereon.

BACKGROUND OF THE INVENTION

Epoxy resins are an important class of thermosetting compounds. Theyhave diverse applications and are widely used in adhesives, structuralmaterials, lacquer, ceramic manufacturing, printed circuit boards,microelectronics packaging, aerospace industry, etc. Epoxy resinsusually are hardened or cured by a cross-linking reaction using one ofthe following three methods. The properties and applications of a curedresin are greatly influenced by the choice of the hardener or the methodof curing.

Method 1: An epoxy resin reacts with itself (i.e., homopolymerizes) viaa ring-opening polymerization mechanism of the epoxy groups. Theself-curing of epoxy resins usually requires an elevated temperature butcan be initiated with either a Lewis acid or a Lewis base catalyst (asopposed to a curing agent).

Method 2: An epoxy resin can be cured with a cyclic acid anhydride. Theanhydride can react with the epoxy group, pendant hydroxyls, or residualwater to form a carboxylate intermediate, which then reacts with theepoxy group, causing a self-perpetuating reaction between the anhydrideand the epoxy resin. Catalytic amounts of tertiary amines are commonlyused as additives as they facilitate the opening of the anhydride.

Method 3: An epoxy resin reacts with a polyvalent nucleophilic reagent,e.g., a polyamine, at the room temperature. For instance, the ringopening of the epoxy ring with a primary or secondary amine generates astable C—N bond, which is then cured to form a three dimensional networkstructure with a high crosslinking density. The epoxy resin canpotentially react with potentially every amine group containing anactive hydrogen atom, so that, e.g., a simple diamine (NH₂—R—NH₂) actsas a tetrafunctional cross-linker and reacts with four epoxy groups.Similar to polyamines, polythiol compounds (HS—R—SH) can also react withepoxy groups to form C—S bonds. The reaction of a thiol group with theepoxy group is greatly facilitated by the presence of a catalytic amountof base, such as a tertiary amine, to result in a faster curing processeven at the room temperature.

The most common epoxy resin formulations consist of a diepoxide (resin)and a polyamine compound (curing agent or hardener), which form apolymeric network of essentially infinite molecular weight. Thecombination of “resin” and “curing agent” sometimes is referred to as“after curing (cured) epoxy resin,” “after curing (cured) resin”, orsimply “resin” or “epoxy resin.” The widespread utility of such epoxyformulations is due to their excellent processability prior to curingand their excellent post-cure adhesion, mechanical strength, thermalprofile, electronic properties, chemical resistance, etc. Furthermore,the high-density, infusible three-dimensional network of epoxies makesit an extremely robust material, resulting in it being the material ofchoice for many long-term applications. At the same time, thisdurability makes its removal, recycling and reworkability notoriouslydifficult, raising concerns about the longevity of epoxy-based materialsin the environment. The cross-linking reactions that occur with twoconvertibly used component epoxies are essentially irreversible.Therefore, the material cannot be easily dissolved, or melted andreshaped without decomposition of the material. The epoxy resin, due toits excellent physical and mechanical properties, electrical insulation,and adhesive performance, is widely used in composite materials, castingparts, electronics, coating, etc. In particular, fiber reinforced epoxyresin composite materials, especially carbon fiber composites, have beenwidely used in aerospace, automobile, train, ship, wind energy tidalenergy, sporting goods and other industries. It has been estimated thatby 2015, global composite material production capacity willsignificantly increase, and exceed 10 million tons. However, how to dealwith and recycle the waste of fiber composites has become a worldwideproblem that prevents the fiber composite industry's growth, therebyconstraining the sustainable development of fiber composites.

By far, the recycling process of fiber composite materials have beenroughly reported in the following ways: 1. High temperature thermaldegradation (Thermochimica Acta 2007(454): 109-115), which can recyclecomposite material to obtain clean filler and fiber, but requires hightemperature processing and high standard equipment; 2. Fluidized bed(Applied surface science 2008(254): 2588-2593), which requires hightemperature processing to recycle and obtain the clean fiber; 3.Supercutical fluid (water (Materials and design 2010(31):999-1002),alcohol (Ind.eng.chem.res. 2010(49): 4535-4541) or carbon dioxide(CN102181071), for degrading epoxy resin system, which is still in thelaboratory stage and far from practical industrialization; 4. Use nitricacid (Journal of applied polymer science, 2004 (95): 1912-1916) todegrade the epoxy resin and obtain fiber with clean surface, which hasstrong corrosion resistance of acid like nitric acid, requires highstandard equipment, and results in low operating security, high recyclecost, and difficult post-processing. Generally, these methods have theirlimitations in varying degrees, existing disadvantages of fibershortening, performance degradation, environmental pollution, and highrecycling cost and so on, therefore, effective and feasible method forthe recycling of waste composite materials is still an issue to beaddressed in composites field.

SUMMARY OF THE INVENTION

To solve the problems or overcome the deficiencies of the existingtechnologies, the present invention provides, among others, degradableepoxy curing agents, the polymers and reinforced composite materialsderived from those curing agents and epoxy resin, methods for degradingthose polymers and reinforced composites. The degradable compositesprovided by this invention have excellent mechanical properties, and aresuitable for a variety of applications in the field of composites. Underspecific conditions, the composite material can be degraded, and thematrix degradation products of reinforcing material and epoxy resin canbe separated and recovered. Furthermore, the degradation and recoverymethod of reinforced composite is economic, easy to control and can beproceed under relatively mild reaction conditions.

Accordingly, this present invention provides the following technicalsolutions.

In one aspect, the present invention provides curing agent comprising acompound of Formula I or a salt thereof:

In Formula I:

n is an integer greater than 1;

A is alkylene, alkylene-hetero-alkylene, alkenylene,alkenylene-hetero-alkenylene, alkylene-hetero-alkenylene, alkynylene,cycloalkylene, alkylene-cycloalkylene, alkylene-cycloalkylene-alkylene,alkenylene-cycloalkylene, alkenylene-cycloalkylene-alkenylen,alkylene-cycloalkylene-alkenylene, alkynylene-cycloalkylene,alkynylene-cycloalkylene-alkynylene, heterocycloalkylene,alkylene-heterocycloalkylene, alkylene-heterocycloalkylene-alkylene,alkenylene-heterocycloalkylene,alkenylene-heterocycloalkylene-alkenylene,alkylene-heterocycloalkylene-alkenylene, alkynylene-heterocycloalkylene,alkynylene-heterocycloalkylene-alkynylene, cycloalkenylene,alkylene-cycloalkenylene, alkylene-cycloalkenylene-alkylene,alkenylene-cycloalkenylene, alkenylene-cycloalkenylene-alkenylene,alkylene-cycloalkenylene-alkenylene, alkynylene-cycloalkenylene,alkynylene-cycloalkenylene-alkynylene, heterocycloalkenylene,alkylene-heterocycloalkenylene, alkylene-heterocycloalkenylene-alkylene,alkenylene-heterocycloalkenylene,alkenylene-heterocycloalkenylene-alkenylene,alkylene-heterocycloalkenylene-alkenylene,alkynylene-heterocycloalkenylene,alkynylene-heterocycloalkenylene-alkynylene, arylene, arylene-X-arylene,alkylene-arylene, alkylene-arylene-alkylene, alkenylene-arylene,alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene,alkynylene-arylene, alkynylene-arylene-alkynylene, heteroarylene,heteroarylene-X-heteroarylene, heteroarylene-X-arylene,alkylene-heteroarylene, alkylene-heteroarylene-alkylene,alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene,alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, oralkynylene-heteroarylene-alkynylene;

X is alkylene, alkenylene, oxygen, sulfur, nitrogen, sulfoxide, sulfone,carbonyl, —C(O)O—, —OC(O)O—, —OC(O)NH—, —C(O)NH—, or —HNC(O)NH—;

each B independently is hydrogen, alkyl, cycloalkyl, heterocyclic,heterocycloalkyl, alkenyl, cycloalkenyl, aryl, arylalkyl, heteroaryl,heteroarylalkyl, alkyl-hetero-alkyl, alkyl-hetero-alkenyl, or alkynyl;

or, A and at least one B, together with the carbon atom to which theyare bonded, form a saturated or unsaturated ring optionally containingat least one hetero ring atom of O, S, N, or P;

or, at least two B groups, together with A and carbon atoms to which Aand B groups are bonded, form a saturated or unsaturated ring optionallycontaining at least one hetero ring atom of O, S, N, or P.

The ring can be, e.g., 3- to 9-membered (e.g., 3- to 8-, 4- to 8-, 4- to7-, 5- to 7-, 5- to 6-, or 6- to 7-). An unsaturated ring can bearomatic or non-aromatic.

In some embodiments, n is 2, 3, or 4 in Formula I. In some otherembodiments, n is 2 or 3. Of course, n can be 2, 3, 4, 5, 6, 7, or 8, orup to 100 or even higher, as long as a compound with that number for nis chemically possible or feasible.

In some other embodiments, A in Formula I is alkylene,alkylene-hetero-alkylene, alkenylene, alkenylene-hetero-alkenylene,alkylene-hetero-alkenylene, cycloalkylene, heterocycloalkylene, arylene,arylene-X-arylene, alkylene-arylene, alkylene-arylene-alkylene,alkenylene-arylene, alkenylene-arylene-alkenylene,alkylene-arylene-alkenylene, alkynylene-arylene,alkynylene-arylene-alkynylene, heteroarylene,heteroarylene-X-heteroarylene, heteroarylene-X-arylene,alkylene-heteroarylene, alkylene-heteroarylene-alkylene,alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene,alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, oralkynylene-heteroarylene-alkynylene; and X is alkylene, oxygen, sulfur,nitrogen, sulfoxide (i.e., —SO—), sulfone (i.e., —SO₂—), or —OC(O)O—.For example, A can be alkylene, arylene, heteroarylene,arylene-X-arylene, heteroarylene-X-heteroarylene, orheteroarylene-X-arylene. Or, A can be alkylene, arylene, orarylene-X-arylene. Specific examples of A include methylene, ethylene,propylene, phenylene, and phenylene-X-phenylene. Specific examples of Xinclude oxygen, sulfur, nitrogen, sulfoxide, and sulfone. When oneterminal of A is not substituted or bonded with any —CB═N—NH₂ group,then A in Formula I becomes, e.g., alkyl, alkyl-hetero-alkylene,alkenyl, alkenyl-hetero-alkenylene, alkyl-hetero-alkenylene, aryl,aryl-X-arylene, alkyl-arylene, alkyl-arylene-alkylene, alkenyl-arylene,alkenyl-arylene-alkenylene, alkyl-arylene-alkenylene, alkynyl-arylene,alkynyl-arylene-alkynylene, heteroarylene,heteroarylene-X-heteroarylene, heteroarylene-X-arylene,alkylene-heteroarylene, alkyl-heteroarylene-alkylene,alkenyl-heteroarylene, alkenyl-heteroarylene-alkenylene,alkyl-heteroarylene-alkenylene, alkynyl-heteroarylene, oralkynyl-heteroarylene-alkynylene

When A has more than one carbon atoms, the different —CB═N—NH₂ groupscan be on, or bonded to, the same or different carbon atoms of A. As anexample to illustrate the possibility, if A is propylene and n is 2, thetwo —CB═N—NH₂ groups can be both on a same carbon atom of the propylenegroup, or on different carbon atoms of the propylene group (e.g., 1,3 or1,2 carbon atoms). Or, if A is ethylene and n is 2, the two

In still some other embodiments, each B independently is hydrogen,alkyl, alkyl-hetero-alkyl, alkenyl, alkenyl-hetero-alkenyl,alkenyl-hetero-alkyl, alkyl-hetero-alkenyl, or alkynyl. Particularly,each B independently can be hydrogen or alkyl. When two or more B groupsin Formula I are of the same type, e.g., alkyl, they can still bedifferent by having different numbers of carbon atoms or with differentsubstituents.

In yet still some other embodiments, A and at least one B, together withthe carbon atom to which they are bonded, form a 3- to 8-memberedsaturated or unsaturated ring optionally containing at least one heteroring atom. Examples of the hetero atom include 0, S, N, or P. The ringcan be optionally substituted. In this case, the above specificdefinitions for A and B, when they form a ring, do not apply.

Examples of compounds of Formula I include

In another aspect, the present invention provides a curing agentcomprising a compound of Formula II or a salt thereof:

In Formula II,

n is an integer greater than 1;

each A independently is alkylene, alkylene-hetero-alkylene, alkenylene,alkenylene-hetero-alkenylene, alkylene-hetero-alkenylene, alkynylene,cycloalkylene, alkylene-cycloalkylene, alkylene-cycloalkylene-alkylene,alkenylene-cycloalkylene, alkenylene-cycloalkylene-alkenylen,alkylene-cycloalkylene-alkenylene, alkynylene-cycloalkylene,alkynylene-cycloalkylene-alkynylene, heterocycloalkylene,alkylene-heterocycloalkylene, alkylene-heterocycloalkylene-alkylene,alkenylene-heterocycloalkylene,alkenylene-heterocycloalkylene-alkenylene,alkylene-heterocycloalkylene-alkenylene, alkynylene-heterocycloalkylene,alkynylene-heterocycloalkylene-alkynylene, cycloalkenylene,alkylene-cycloalkenylene, alkylene-cycloalkenylene-alkylene,alkenylene-cycloalkenylene, alkenylene-cycloalkenylene-alkenylene,alkylene-cycloalkenylene-alkenylene, alkynylene-cycloalkenylene,alkynylene-cycloalkenylene-alkynylene, heterocycloalkenylene,alkylene-heterocycloalkenylene, alkylene-heterocycloalkenylene-alkylene,alkenylene-heterocycloalkenylene,alkenylene-heterocycloalkenylene-alkenylene,alkylene-heterocycloalkenylene-alkenylene,alkynylene-heterocycloalkenylene,alkynylene-heterocycloalkenylene-alkynylene, arylene, alkylene-arylene,alkylene-arylene-alkylene, alkenylene-arylene,alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene,alkynylene-arylene, alkynylene-arylene-alkynylene, heteroarylene,alkylene-heteroarylene, alkylene-heteroarylene-alkylene,alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene,alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, oralkynylene-heteroarylene-alkynylene;

B is hydrogen, alkyl, cycloalkyl, heterocyclic, heterocycloalkyl,alkenyl, cycloalkenyl, aryl, heteroaryl, alkyl-hetero-alkyl, alkynyl, oralkyl-hetero-alkynyl; and

C is hydrogen, alkyl, cycloalkyl, heterocyclic, heterocycloalkyl,alkenyl, cycloalkenyl, aryl, heteroaryl, alkyl-hetero-alkyl, or alkynyl;

or, C and B, together with A and the carbon atom to which they arebonded respectively, form a saturated or unsaturated ring optionallycontaining at least one hetero ring atom of O, S, N or P. The ring canbe, e.g., 3- to 9-membered (e.g., 3- to 8-, 4- to 8-, 4- to 7-, 5- to7-, 5- to 6-, or 6- to 7-). An unsaturated ring can be aromatic ornon-aromatic.

In some embodiments, n is 2, 3, or 4 in Formula I. In some otherembodiments, n is 2 or 3. Of course, n can be 2, 3, 4, 5, 6, 7, or 8, orup to 100 or even higher, as long as a compound with that number for nis chemically possible or feasible.

In some embodiments, each A independently is alkylene, alkenylene,alkylene-hetero-alkylene, arylene, alkylene-arylene,alkylene-arylene-alkylene, alkenylene-arylene,alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene,alkynylene-heteroarylene, or alkynylene-heteroarylene-alkynylene. Whentwo or more A groups in Formula II are of the same type, e.g., alkyl,they can still be different by having different carbon atoms or withdifferent substituents.

In some other embodiments, each A independently is alkylene oralkenylene.

In still some other embodiments, B is hydrogen, alkyl, cycloalkyl,heterocyclic, heterocycloalkyl, alkenyl, aryl, heteroaryl,alkyl-hetero-alkyl. Specifically, B can be hydrogen, alkyl, or alkenyl.

In yet still some other embodiments, C is hydrogen or alkyl.

In some other embodiments, C and B, together with A and the carbon atomto which they are bonded respectively, form a saturated or unsaturatedring optionally containing at least one hetero ring atom of O, S, N, orP. The ring can be, e.g., 3- to 9-membered (e.g., 3- to 8, 4- to 8-, 4-to 7-, 5- to 7-, or 6- to 7-).

Examples of the compound of Formula II include

As mentioned above, salts of the compounds of Formula I or II are alsowithin the scope of this invention. To form such a salt, either one ormore of the terminal amino groups in each of the compounds or theinternal nitrogen atom (i.e., ═N—) can be reacted with an acid, e.g.,hydrochloride acid or sulfuric acid, to form a tertiary amine salt. Forillustration purpose, examples of such salts include

The curing agents described above can be useful for curing an epoxyresin to produce a degradable cured epoxy resin.

Another aspect of the present invention provides a degradablecross-linked polymer comprising a cleavable cross-linking group derivedfrom a curing agent described above and an epoxy resin, wherein at leastone amino group in the curing agent is fully reacted to lose bothhydrogen atoms and form two bonds with the epoxy resin. As used herein,the term “derived” means that when a curing agent described abovecontaining a compound of Formula I or II cures a polymer, e.g., an epoxyresin, the curing agent would lose at least two active hydrogen atoms ofone or two terminal amino groups in the curing agent. For example, oneamino group can completely lose its two active hydrogen atoms so thatthe nitrogen would form to bonds with the cured resin (as shown below inFormulae I-b and II-b as examples), forming the cross-linked polymer.Alternatively, two amino groups can each lose one active hydrogen toform (and derive to) a linking group shown below in Structures I-c andII-c as examples.

In some embodiments, the epoxy resin comprises a glycidyl ether epoxyresin, glycidyl ester epoxy resin, glycidyl epoxy amine epoxy resin,trifunctional epoxy resin, tetrafunctional epoxy resin, novolac epoxyresin, o-cresol formaldehyde epoxy resin, aliphatic epoxy resin,alicyclic epoxy resin, or nitrogen-containing epoxy resin.

In some other embodiments, the cleavable cross-linking group is derivedfrom

Examples of the cross-linking group include, but are not limited to,

In some examples of the linking group derived from a compound of FormulaI or II described above, at least one amino group of the compound isfully reacted to lose both hydrogen atoms; whereas in some otherexamples, no terminal amino group is required to fully react and loseboth active hydrogen atoms.

Another aspect of this invention provides a recyclable prepreg (i.e.,pre-impregnated) composition or reinforced composite material,comprising a curing agent as described above, an epoxy resin, anauxiliary material and a reinforcing material. In this recyclableprepreg composition or reinforced composite material, the epoxy resincomprises glycidyl ether epoxy resin, glycidyl ester epoxy resin,glycidyl epoxy amine epoxy resin, trifunctional epoxy resin,tetrafunctional epoxy resin, novolac epoxy resin, o-cresol formaldehydeepoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, ornitrogen-containing epoxy resin; the reinforcing material comprisescarbon nanotube, boron nitride nanotube, carbon black, metalnano-particle, metal oxide nanoparticle, organic nanoparticle, ironoxide, glass fiber, carbon fiber, natural fiber, synthetic fiber, orfabrics made therefrom; and the auxiliary material comprisesaccelerator, diluent, plasticizer, toughening agent, thickening agent,coupling agent, defoamer, flatting agent, ultraviolet absorber,antioxidant, brightener, fluorescent agent, pigment, or filler. For adetailed description of the above-mentioned epoxy resin, please seeEpoxy Resins: Chemistry and Technology (Second Ed.). New York: MarcelDekker Inc. (ISBN 0-8247-7690-9), which is incorporated herein byreference in its entirety.

Still another aspect of this invention provides a method for degrading adegradable cross-linked polymer, a recyclable prepreg composition, or areinforced composite material described above. This method includes thesteps, in the order, of (1) under the heating and stirring conditions,immersing the polymer in a mixed acid and solvent system to obtain adegradation solution; and (2) using an alkaline solution to control thepH of the degradation solution. The method may further include, as anoptional step, washing and drying the precipitate and degradationsolution after pH adjustment in step (2).

In some embodiments of the methods, the acid comprises a hydrochloricacid, hydrobromic acid, hydrofluoric acid, acetic acid, trifluoroaceticacid, lactic acid, formic acid, propionic acid, citric acid,methanesulfonic acid, p-toluenesulfonic acid, nitric acid, sulfuricacid, sulfurous acid, phosphoric acid, perchloric acid, benzoic acid,salicylic acid, or phthalic acid; the alkali comprises lithiumhydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide,sodium carbonate, sodium bicarbonate, potassium carbonate, potassiumbicarbonate, or ammonia; each of the solvent for immersing the polymerin step (1) and the solvent for the alkaline solution in step (2)independently comprises methanol, ethanol, ethylene glycol, propanol,isopropanol, butanol, isobutanol, t-butanol, pentanol, hexanol,heptanol, octanol, nonanol, benzyl alcohol, phenethyl alcohol,p-hydroxymethyl benzene, m-hydroxymethyl benzene, o-hydroxy benzene,p-hydroxyethyl benzene, m-hydroxyethyl benzene, o-hydroxyethyl benzene,water, N,N-dimethylformamide, N,N-dimethylacetamide,N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, methyltetrahydrofuran, glycerol, or dioxane.

In some other embodiments, the heating temperature is in the range of80˜150° C., and the heating time is 4˜8 hours, and the massconcentration of the acid in the solvent system is 0.5˜20% (w/w); and instep (2), the temperature is in the range of 5˜50° C., the final pH is6˜12, and the mass concentration of the alkali in the solvent is 5˜30%(w/w). In still some other embodiments, in step (1), the heatingtemperature is 15˜400° C., heating time is 1˜600 hours, the massconcentration of acid in the solvent is 0.1˜100%.

Yet still another aspect of this invention provides a method forpreparing a curing agent of Formula I or II as described above. Themethod comprises the step of reacting a compound of Formula I-a or II-awith hydrazine. A and B in Formula I-a, and A, B and C in Formula II-a,are the same as those defined above or in the annexed claims forFormulae I and II.

In some embodiments of the methods, the mole ratio of the compound ofFormula I-a or the compound of Formula II-a to hydrazine is 1:2˜100, andthe reaction is conducted at a temperature of −20˜150° C.

As used herein, the term “alkyl,” when used alone or as part of a largermoiety (e.g., as in “cycloalkenylalkyl”), refers to a saturatedaliphatic hydrocarbon group. It can contain 1 to 12 (e.g., 1 to 8, 1 to6, or 1 to 4) carbon atoms. As a moiety, it can be denoted as—C_(n)H_(2n+1). An alkyl group can be straight or branched. Examples ofalkyl groups include, but are not limited to, methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-heptyl,and 2-ethylhexyl. An alkyl group can be substituted (i.e., optionallysubstituted) with one or more substituents. When an alkyl is preceded bya carbon-number modifier, e.g., C₁₋₈, its means the alkyl group contains1 to 8 carbon atoms.

As used herein, the term “alkylene,” when used alone or as part of alarger moiety (e.g., as in “arylaalkyleneoxy”), refers to a saturatedaliphatic hydrocarbon group with two radical points for forming twocovalent bonds with two other moieties. It can contain 1 to 12 (e.g., 1to 8, 1 to 6, or 1 to 4) carbon atoms. As a moiety, it can be denoted as—C_(n)H_(2n)—. Examples of an alkylene group include, but are notlimited to, methylene (—CH₂—), ethylene (—CH₂CH₂—), and propylene(—CH₂CH₂CH₂—). When an alkylene is preceded by a carbon-number modifier,e.g., C₂₋₈, it means the alkylene group contains 2 to 8 carbon atoms.

As used herein, the term “alkynyl,” when used alone or as part of alarger moiety (e.g., as in “alkynylalkyl”), refers to an aliphatichydrocarbon group with at least one triple bond. It can contain 2 to 12(e.g., 2 to 8, 2 to 6, or 2 to 4) carbon atoms. An alkynyl group can bestraight or branched. Examples of an alkynyl group include, but are notlimited to, propargyl and butynyl. When an alkynyl is preceded by acarbon-number modifier, e.g., C₂₋₈, it means the alkynyl group contains2 to 8 carbon atoms.

As used herein, the term “alkenyl,” when used alone or as part of alarger moiety (e.g., as in “alkenylalkyl”), refers to an aliphatichydrocarbon group with at least one double bond. It can contain 2 to 12(e.g., 2 to 8, 2 to 6, or 2 to 4) carbon atoms. An alkenyl group withone double bond can be denoted as —C_(n)H_(2n−1), or —C_(n)H_(2n−3) withtwo double bonds. Like an alkyl group, an alkenyl group can be straightor branched. Examples of an alkenyl group include, but are not limitedto, allyl, isoprenyl, 2-butenyl, and 2-hexenyl. When an alkylene ispreceded by a carbon-number modifier, e.g., C₃₋₈, it means the alkylenegroup contains 3 to 8 carbon atoms.

As used herein, the term “cycloalkyl,” when used alone or as part of alarger moiety (e.g., as in “cycloalkylalkyl”), refers to a saturatedcarbocyclic mono-, bi-, or tri-cyclic (fused or bridged or spiral) ringsystem. It can contain 3 to 12 (e.g., 3 to 10, or 5 to 10) carbon atoms.Examples of cycloalkyl groups include, but are not limited to,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,adamantyl, norbornyl, cubyl, octahydro-indenyl, decahydro-naphthyl,bicyclo[3.2.1]octyl, bicyclo[2.2.2]octyl, bicyclo[3.3.1]nonyl,bicyclo[3.3.2.]decyl, bicyclo[2.2.2]octyl, adamantyl, azacycloalkyl, or((aminocarbonyl)cycloalkyl)cycloalkyl. When a cycloalkyl is preceded bya carbon-number modifier, e.g., C₃₋₈, its means the alkyl group contains3 to 8 carbon atoms.

As used herein, the term “cycloalkenyl,” when used alone or as part of alarger moiety (e.g., as in “cycloalkenylalkyl”), refers to anon-aromatic carbocyclic ring system having one or more double bonds. Itcan contain 3 to 12 (e.g., 3 to 10, or 5 to 10) carbon atoms. Examplesof cycloalkenyl groups include, but are not limited to, cyclopentenyl,1,4-cyclohexa-di-enyl, cycloheptenyl, cyclooctenyl, hexahydro-indenyl,octahydro-naphthyl, cyclohexenyl, cyclopentenyl, bicyclo[2.2.2]octenyl,orbicyclo[3.3.1]nonenyl.

As used herein, the term “heterocycloalkyl,” when used alone or as partof a larger moiety (e.g., as in “heterocycloalkylalkyl”), refers to a 3-to 16-membered mono-, bi-, or tri-cyclic (fused or bridged or spiral))saturated ring structure, in which one or more of the ring atoms is aheteroatom (e.g., N, O, S, or combinations thereof). In addition to theheteroatom(s), the heterocycloalkyl can contain 3 to 15 carbon atoms(e.g., 3 to 12 or 5 to 10). Examples of a heterocycloalkyl groupinclude, but are not limited to, piperidyl, piperazyl,tetrahydropyranyl, tetrahydrofuryl, 1,4-dioxolanyl, 1,4-dithianyl,1,3-dioxolanyl, oxazolidyl, isoxazolidyl, morpholinyl, thiomorpholyl,octahydrobenzofuryl, octahydrochromenyl, octahydrothiochromenyl,octahydroindolyl, octahydropyrindinyl, decahydroquinolinyl,octahydrobenzo[b]thiopheneyl, 2-oxa-bicyclo[2.2.2]octyl,l-aza-bicyclo[2.2.2]octyl, 3-aza-bicyclo[3.2.1]octyl, and2,6-dioxa-tricyclo[3.3.1.03,7]nonyl. A monocyclic heterocycloalkyl groupcan be fused with a phenyl moiety such as tetrahydroisoquinoline. When aheterocycloalkyl is preceded by a carbon-number modifier, e.g., C₄₋₈, itmeans the heterocycloalkyl group contains 4 to 8 carbon atoms.

As used herein, the term “hetero,” when used alone or as part of alarger moiety (e.g., as in “heterocyclo,” “heterocycloalkyl,”“heterocycloalkylene” or “heteroaryl”), refers to a hetero atom or groupthat is —O—, —S—, —NH—, —C(═O)—, or P.

When being a hetero ring atom, P can take the form of —P—, —P(O)—,—P(O)₂—, or —P(O)₂R—.

As used herein, the term “aryl,” when used alone or as part of a largermoiety (e.g., as in “arylkyl,” or “arylkoxy”), refers to a monocyclic(e.g., phenyl), bicyclic (e.g., indenyl, naphthalenyl, ortetrahydronaphthyl), and tricyclic (e.g., fluorenyl,tetrahydrofluorenyl, tetrahydroanthracenyl, or anthracenyl) ring systemin which the monocyclic ring system is aromatic (e.g., phenyl) or atleast one of the rings in a bicyclic or tricyclic ring system isaromatic (e.g., phenyl). The bicyclic and tricyclic groups include, butare not limited to, benzo-fused 2- or 3-membered carbocyclic rings. Forinstance, a benzo-fused group includes phenyl fused with two or moreC₄₋₈ carbocyclic moieties.

As used herein, the term “heteroaryl” refers to a monocyclic, bicyclic,or tricyclic ring system having 5 to 15 ring atoms wherein at least oneof the ring atoms is a heteroatom (e.g., N, O, S, or combinationsthereof) and when the monocyclic ring system is aromatic or at least oneof the rings in the bicyclic or tricyclic ring systems is aromatic. Itcan contain 5 to 12 or 8 to 10 ring atoms. A heteroaryl group includes,but is not limited to, a benzo-fused ring system having 2 to 3 rings.For example, a benzo-fused group includes benzo fused with one or two 4-to 8-membered heterocycloalkyl moieties (e.g., indolizyl, indolyl,isoindolyl, 3H-indolyl, indolinyl, benzo[b]furyl, benzo[b]thiophenyl,quinolinyl, or isoquinolinyl). Some examples of heteroaryl are pyridyl,IH-indazolyl, furyl, pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl,tetrazolyl, benzofuryl, isoquinolinyl, benzithiazolyl, xanthenyl,thioxanthenyl, phenothiazinyl, dihydroindolyl, benzo[1,3]dioxolyl, benzo[b] furyl, benzo [bjthiophenyl, indazolyl, benzimidazolyl,benzthiazolyl, puryl, quinolinyl, quinazolinyl, phthalazyl, quinazolyl,quinoxalyl, isoquinolinyl, 4H-quinolizyl, benzo-1,2,5-thiadiazolyl, and1,8-naphthyridyl.

As used herein, the suffix “-ene” is used to describe a bivalent groupwith two radical points for forming two covalent bonds with two othermoieties. In other words, any of the terms as defined above can bemodified with the suffix “-ene” to describe a bivalent version of thatmoiety. For example, a bivalent aryl ring structure is “arylene,” abivalent benzene ring structure is “phenylene,” a bivalent heteroarylring structure is “heteroarylene,” a bivalent cycloalkyl ring structureis a “cycloalkylene,” a bivalent heterocycloalkyl ring structure is“heterocycloalkylene,” a bivalent cycloalkenyl ring structure is“cycloalkenylene,” a bivalent alkenyl chain is “alkenylene,” and abivalent alkynyl chain is “alkynylene.”

As used herein, the term “optionally” (e.g., as in “optionallysubstituted with”) means that the moiety at issue is either substitutedor not substituted, and that the substitution occurs only when it ischemically feasible. For instance, H cannot be substituted with asubstituent and a covalent bond or —C(═O)— group cannot be substitutedwith a substituent.

As used herein, an “oxo” or “oxide” group refers to ═O.

As used herein, a “carbonyl” group refers to —C(O)— or —C(═O)—.

As used herein, the term “substituted,” whether preceded by the term“optionally” or not, refers to the replacement of hydrogen radicals in agiven structure with the radical of a specified substituent. Specificsubstituents are described above in the definitions and below in thedescription of compounds and examples thereof. Unless otherwiseindicated, an optionally substituted group can have a substituent ateach substitutable position of the group, and when more than oneposition in any given structure can be substituted with more than onesubstituent selected from a specified group, the substituent can beeither the same or different in every position. A ring substituent, suchas a heterocycloalkyl, can be bound to another ring, such as acycloalkyl, to form a spiro-bicyclic ring system, e.g., both rings shareone common atom. As one of ordinary skill in the art will recognize,combinations of substituents envisioned by this invention are thosecombinations that result in the formation of stable or chemicallyfeasible compounds.

For convenience and as commonly understood, the term “optionallysubstituted” only applies to the chemical entities that can besubstituted with suitable substituents, not to those that cannot besubstituted chemically.

As used herein, the term “or” can mean “or” or “and.”

DETAILED DESCRIPTION OF THE INVENTION

The following examples are provided for illustration only, and notintended to be limiting in any aspect.

Example 1 Preparation of Curing Agent 1

70 g ethanol and 36.7 g 85% hydrazine hydrate were placed in the flaskreactor. 25 g 2,4-pentandione dissolved in 40 g ethanol was addeddropwise while stirring at the room temperature for one hour. Then thesolution was heated to reflux for 5˜6 hours. The solution wasconcentrated at reduced pressure, and then the residue solid was washedwith petroleum ether, filtered and dried to give 10 g white solid.

MP: 104˜106° C.

¹H-NMR (CDCl₃, 400 MHz): 2.27 (s, 6H), 5.82 (s, 1H).

Example 2 Preparation of Curing Agent 1

70 g ethanol and 36.7 g 85% hydrazine hydrate were placed in the flaskreactor, 25 g 2,4-pentandione dissolved in 40 g ethanol was addeddropwise while stirring at the room temperature in one hour, then thesolution was heated to 60˜65° C. After 5˜6 hours, the solution wasconcentrated at reduced pressure, then the residue solid was washed withpetroleum ether, filtered and dried to give 10.7 g white solid.

Example 3 Preparation of Curing Agent 1

70 g ethanol and 36.7 g 85% hydrazine hydrate were placed in the flaskreactor. 25 g 2,4-pentandione dissolved in 40 g ethanol was addeddropwise while stirring at the room temperature for one hour. Then thesolution was heated to 40˜45° C. After 5˜6 hours, the solution wasconcentrated, and then the residue solid was washed with petroleumether, filtered and dried to give 11.5 g white solid.

Example 4 Preparation of Curing Agent 1

70 g ethanol and 36.7 g 85% hydrazine hydrate were placed in the flaskreactor. 25 g 2,4-pentandione dissolved in 40 g ethanol was addeddropwise while stirring at the room temperature for one hour. Then thesolution was heated to the room temperature. After 5˜6 hours, thesolution was concentrated, and then the residue solid was washed withpetroleum ether, filtered and dried to give 13.4 g white solid.

Example 5 Preparation of Curing Agent 1

70 g ethanol and 36.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C. 25 g 2,4-Pentandione dissolved in 40 gethanol was added dropwise while stirring at 5˜10° C. for one hour.After 5˜6 hours below 10° C., the solution was concentrated, and theresidue solid was washed with petroleum ether, then filtered and driedto give 15 g white solid.

Example 6 Preparation of Curing Agent 2

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor. 13.4 g 1,4-phthalaldehyde dissolved in 370 g ethanol was addeddropwise while stirring at the room temperature for one hour. Thesolution was stirring at the room temperature for 5˜6 hours, and thenfiltered. The filter cake was washed with ethanol and dried to give 13.9g yellow solid.

MP: 158˜166° C.

¹H-NMR (400 MHz, d₆-DMSO): 7.67 (s, 2H), 7.42 (s, 4H), 6.76 (s, 4H).

Example 7 Preparation of Curing Agent 2

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor. 13.4 g 1,4-phthalaldehyde dissolved in 370 g ethanol was addeddropwise while stirring at the room temperature for one hour. Then thesolution was heated to 40˜45° C. After 5˜6 hours, the solution wascooled to room temperature, filtered, and the filter cake was washedwith ethanol and dried to give 13.5 g yellow solid.

Example 8 Preparation of Curing Agent 2

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor. 13.4 g 1,4-phthalaldehyde dissolved in 370 g ethanol was addeddropwise while stirring at the room temperature for one hour. Then thesolution was heated to 60˜65° C. After 5˜6 hours, the solution wascooled to room temperature, filtered, and the filter cake was washedwith ethanol and dried to give 11 g yellow solid.

Example 9 Preparation of Curing Agent 2

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor. 13.4 g 1,4-phthalaldehyde dissolved in 370 g ethanol was addeddropwise while stirring at the room temperature for one hour. Then thesolution was heated to reflux for 5˜6 hours, the solution was cooled tothe room temperature, filtered, and the filter cake was washed withethanol and dried to give 10.3 g yellow solid.

Example 10 Preparation of Curing Agent 2

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C., 13.4 g 1,4-phthalaldehyde dissolved in370 g ethanol was added dropwise while stirring at 5˜10° C. for onehour. After 5˜6 hours below 10° C., and the solution was cooled to thetemperature, filtered, the filter cake was washed with ethanol and driedto give 14.6 g yellow solid.

Example 11 Preparation of Curing Agent 3

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C., 10.8 g 1,4-benzoquinone dissolved in 180g ethanol was added dropwise while stirring at 5˜10° C. for one hour.The reaction was heated to reflux for 5˜6 hours, the solution wasconcentrated at reduced pressure, and the filter cake was washed withethanol, filtered and dried to give 8.4 g brown solid.

MP: 140˜142° C.

¹H-NMR (400 MHz, d₆-DMSO): 6.56 (s, 4H), 5.52 (s, 4H).

Example 12 Preparation of Curing Agent 3

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C., 10.8 g 1,4-benzoquinone dissolved in 180g ethanol was added dropwise while stirring at 5˜10° C. for one hour.The reaction was heated to 60˜65° C. After 5˜6 hours, the solution wasconcentrated at reduced pressure, and the solid was washed with ethanol,filtered and dried to give 9.4 g brown solid.

Example 13 Preparation of Curing Agent 3

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C., 10.8 g 1,4-benzoquinone dissolved in 180g ethanol was added dropwise while stirring at 5˜10° C. for one hour.The reaction was heated to 40˜45° C. After 5˜6 hours, the solution wasconcentrated at reduced pressure, the solid was washed with ethanol,filtered and dried to give 10.2 g brown solid.

Example 14 Preparation of Curing Agent 3

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C., 10.8 g 1,4-benzoquinone dissolved in 180g ethanol was added dropwise while stirring at 5˜10° C. for one hour.The reaction was heated to room temperature. After 5-6 hours, thesolution was concentrated at reduced pressure, the solid was washed withethanol, filtered and dried to give 11.0 g brown solid.

Example 15 Preparation of Curing Agent 3

20 g ethanol and 14.7 g 85% hydrazine hydrate were placed in the flaskreactor and cooled to 0˜5° C., 10.8 g 1,4-benzoquinone dissolved in 180g ethanol was added dropwise while stirring at 5˜10° C. for one hour.After 5˜6 hours below 10° C., and the solution was concentrated atreduced pressure, and the solid was washed with ethanol, filtered anddried to give 11.8 g brown solid.

Example 16 Preparation of Curing Agent 4

Step 1: To a flask, 250 mL of dichloroethane and aluminum chloride(62.64 g, 0.47 mol) was added. Acetyl chloride (31.58 g, 0.40 mol) wasadded slowly to this mixture at 10° C. and followed by phenyl sulfide(25 g, 0.13 mol). After addition, temperature was increase to roomtemperature and stirred for 8 h. The reaction was quenched by poured to500 mL of crushed ice, the organic layer was extracted with chloroform,and the combined organic layers were washed with a saturated sodiumbicarbonate, followed by a saturated brine solution and dried overanhydrous sodium sulfate and evaporated at vacuum to give compound 2 28g (yield=80%).

¹H-NMR (CDCl₃, 400 MHz) δ 2.57 (6H, s), 7.40 (4H, d), 7.90 (4H, d)

Step 2: To a 500 mL three-necked flask, 18.66 g (0.069 mole) ofbis(4-acetylphenyl)sulfide, 180 g of acetic acid and 40 g ofdichloroethane were fed. To the resulting solution, 0.54 g (0.001 mole)of 20 percent aqueous solution of titanium trichloride was added, and6.21 g (0.054 mole) of 30 percent aqueous hydrogen peroxide solution wasadded thereto dropwise, followed by stirring the resulting mixture for 2hours. To this mixture, 300 mL of water was added, dichloroethane wasevaporated and the resulting mixture was cooled to 10° C., followed bycollection of yielded crystals by filtration. These crystals were washedwith 90 mL of methanol and collected by filtration, purified by columnchromatography on silica gel (petroleum/ethyl acetate=4:1 to 2:1) toprovide the desired product 3 3.6 g. The yield was 19%.

¹H-NMR (CDCl₃, 400 MHz) δ 2.60 (6H, s), 7.78 (4H, d), 8.05 (4H, d)

Step 3: To a 50 mL three-necked flask, 1.7 mL of 85% hydrazine hydrate,15 mL of ethanol were fed. To the resulting solution, 1.6 g (0.006 mole)of product 3 was added partially and stirred at room temperatureovernight. The precipitation was collected by filtration and driedthereof to obtain product 4 1.2 g. The yield was 64%.

¹H-NMR (CDCl₃, 400 MHz): δ 2.11 (6H, s), 5.46 (4H, s) 7.60 (4H, d), 7.72(4H, d).

MP (from DSC): 161.89° C.

Example 17 Preparation of Cured Degradable Epoxy Matrix

10 g Curing Agent 1 in Example 1 (AEW≈3.1 N—H eq./100 g) and 58.9 gliquid bisphenol A epoxy resin of E52D (EEW 0.52˜0.54 eq./100 g) weremixed and stirred evenly at the room temperature. Under 70° C.conditions, the gel time of resin mixture was more than 4 hours, andhalf time of the resin mixture was more than a month at roomtemperature. Appropriate amount of the resin mixture was painted on aglass slide, heated to 125° C. for 2 hours until fully cured to give thesample of cured degradable epoxy resin.

Example 18 Preparation of Cured Degradable Epoxy Matrix

10 g Curing Agent 2 in Example 6 (AEW 2.47 N—H eq./100 g) and 46.4 gliquid bisphenol A epoxy resin of E52D (EEW 0.52˜0.54 eq./100 g) weremixed and stirred evenly at the room temperature. Under 70° C.conditions, the gel time of resin mixture was more than 4 hours, andhalf time of the resin mixture was more than a month at roomtemperature. Appropriate amount of the resin mixture was painted on aglass slide, heated to 120° C. for 2 hours until fully cured to give thesample of cured degradable epoxy resin.

Example 19 Preparation of Cured Degradable Epoxy Matrix

10 g Curing Agent 3 in Example 11 (AEW 2.94 H eq./100 g) and 55.4 gliquid bisphenol F epoxy resin (EEW 0.5˜0.63 eq./100 g) were mixed andstirred evenly at the room temperature. Under 70° C. conditions, the geltime of resin mixture was more than 4 hours, and half time of the resinmixture was more than a month at room temperature. Appropriate amount ofthe resin mixture was painted on a glass slide, heated to 70° C. for 2hours, 125° C. for 2 hours and then 160° C. for 2 hours until fullycured to give the sample of cured degradable epoxy resin.

Example 20 Preparation of Cured Degradable Epoxy Matrix

2.36 g bisphenol A epoxy resin NPEL128 (EEW 0.52˜0.54 eq./100 g) and 1.0g curing agent 4 (AEW 1.27 H eq./100 g) in example 16 were mixed andstirred evenly at the room temperature, and then the mixture was heatedat 130° C. for 4 hours to obtain the cured degradable epoxy resinsample.

Example 21 Degradation of Cured Degradable Epoxy Matrix

0.5 g of the cured sample in Example 17, 10 mL concentrated hydrochloricacid, and 90 mL ethylene glycol were placed in a one-neck round flask,stirred and heated to 180° C., completely degraded after 10 hours togive transparent clear solution, which was neutralized with 20% sodiumhydroxide solution and then precipitated solid was filtered, and thesolid was washed with water and dried to give 0.48 g of degradationproducts of thermoset epoxy resin, mass recovery ratio was 96%.

Example 22 Degradation of Cured Degradable Epoxy Matrix

0.40 g of the cured sample in Example 18, 5 mL concentrated hydrochloricacid, and 90 ml ethylene glycol were placed in an autoclave, stirred andheated to 160° C., completely degraded after 15 hours to givetransparent clear solution, which was neutralized with 20% sodiumhydroxide solution and then precipitated solid was filtered, and thesolid was washed with water and dried to give 0.38 g of degradationproducts of thermoset epoxy resin, mass recovery ratio was 95%.

Example 23 Degradation of Cured Degradable Epoxy Matrix

0.6 g of the cured sample in Example 19, 10 mL concentrated hydrochloricacid, and 90 ml ethylene glycol were placed in a one-neck round flask,stirred and heated to 150° C., completely degraded after 20 hours andtransparent clear solution was obtained, which was neutralized with 20%sodium hydroxide solution and precipitated solid was filtered and thesolid was washed with water and dried to give 0.58 g of degradationproducts of thermoset epoxy resin, mass recovery ratio was 96.6%.

Example 24 Degradation of Cured Degradable Epoxy Matrix

0.3 g cured sample in example 20, 2.5 mL concentrated hydrochloric acidand 50 mL ethylene glycol were placed in a 100 ml three-neck flask,stirred and heated to 155° C., completely degraded after 2 hours, andbrown transparent solution was obtained, which was neutralized with 20%sodium hydroxide solution and precipitated solid was filtered and thesolid was washed with water and dried to give 0.29 g of degradationproducts of thermoset epoxy resin, mass recovery ratio was 96.7%.

Example 25 Preparation and Properties of Degradable Epoxy Matrix

20 g bisphenol A epoxy resin NPEL-128 (EEW 0.52˜0.54 eq./100 g) and 11 gCuring Agent 2 in Example 6 (AEW 2.47 N—H eq./100 g), 20 g CTBN(Carboxyl terminated butadiene acrylonitrile rubber) modified epoxy (EEW0.267˜0.308 eq./100 g) and 26 g MDI modified epoxy resin (EEW 0.33eq./100 g) were mixed in a high speed blender at 70° C. 30 minutes,discharged, and cooled to room temperature, then frozen for storage. Thecuring cycle for the resultant degradable epoxy system is 100° C. for 1hour followed by 125° C. for 2 hours The typical properties of theresultant degradable epoxy system are listed in the below table.

Viscosity @ 70 ± 1° C. (cps) 7800 Gel time @ 115° C. (min) 35~40 Density(g/cm³)  1.2~1.25 Viscosity doubling time (hrs, 20 g@70 ± 1° C.) >4 Tg(Cure Cycle: 100° C. × 1 h + 125° C. × 2 h) 141~147° C. Flexuralstrength (MPa) 109~119 Flexural modulus (GPa) 2.0~2.2 Tensile strength(MPa) 45~55 Tensile modulus (GPa) 2.1~2.3 Elongation (%) 2.1~3.0

Example 26 Degradation of Cured Degradable Epoxy Matrix

10 g cured sample of degradable epoxy system in Example 25, 20 mLconcentrated hydrochloric acid and 190 mL ethylene glycol were placed ina 500-mL three-neck flask, stirred and heated to 155° C., completelydegraded after 48 hour, and brown transparent solution was obtained, thesolution was neutralized with 70% sodium hydroxide solution andprecipitated solid was filtered and the solid was washed with water anddried to give 9.6 g of degradation products of epoxy resin, massrecovery ratio was 96%.

Example 27 Preparation of Degradable Epoxy Carbon Fiber Prepregs

1000 g degradable epoxy system in Example 25 was loaded onto a resinfilm making machine and heated up to 70° C., then melted. Thetemperature of the rubber roller was set to 70° C., then the resin filmmaking machine was switched on to produce adhesive film, and the filmsurface density was 75 g/m². The prepreg preparation equipment wasactivated to adjust the carbon fiber surface density to be 100 g/m². Theprepared epoxy resin film was put into the prepreg preparation equipmentto compound with carbon fibers to prepare the prepregs, the compoundtemperature was 95° C. and compound speed was 9 m/min.

Example 28 Preparation for Degradable Epoxy Resin Laminated Sheets

A mould was placed on a hot-pressing machine, then heated up to 100° C.for standby application. The prepared prepregs in Example 27 weretrimmed to the size of 300 mm×300 mm, then 22 layers of prepregmaterials were laid in the mould with the same direction. The prepregmaterials were clamped and pressured to prepare the composite laminatedsheets. Its parameter of preparation process was as follows: 0.5 MPapressure and 100° C. for 1 hour followed by 125° C. for 2 hours. Theheating electric power was switched off to naturally cool the compositelaminated sheets down to a temperature below 50° C., then the preparedcomposite laminated sheets were removed from the mould. The mechanicalproperties of the composite laminate sheets prepared by this specificembodiment were as follows:

Carbon Fiber Laminates Unit Mean Normalized Standard Carbon FiberContent % 50.3 60 n/a Tensile Strength MPa 1250 1491 GB3354 TensileModulus GPa 111.8 133.4 GB3354 Elongation % 0.43 n/a GB3354 FlexuralStrength MPa 1154.48 1377.11 GB3356 Flexural Modulus GPa 101.1 120.6GB3356 Compression Strength MPa 500.5 597 GB3856 Compression Modulus GPa102.2 122 GB3856 ILSS MPa 41.84 49.9 JC773 IPSS MPa 77.63 n/a GB3355IPSM GPa 4.5 n/a GB3355

Example 29 Degradation of Degradable Carbon Fiber Reinforced Composite

1 g sample of the carbon fiber composite laminate in Example 28 (49.7%resin content), 5 mL concentrated hydrochloric acid and 95 mL ethyleneglycol were placed in a 250 mL three-neck flask, stirred and heated to155° C., completely degraded after 48 hours, filtered. The carbon fiberand the degradation solution were separated, the solution wasneutralized with 70% sodium hydroxide solution to give a precipitatedsolid. The solid was filtered and washed with water, dried to give 0.48g degraded epoxy resin, mass recovery ratio was 96%.

Example 30 Degradation of the Carbon Fiber Fishing Rod

One end of a fishing rod made from degradable carbon fiber prepreg inExample 27 was submerged in a mixture of 10 mL concentrated hydrochloricacid and 190 mL ethylene glycol, heated to 155° C. After 48 hours, thetreated end of the fishing rod was washed with water and dried. Theimmersed part of the rod became disintegrated and remained only in theform of loose carbon fibers. This result confirmed the prepreg materialsof this invention could be degraded under the conditions describedabove.

Other Embodiments of the Invention

The invention has been described above with the reference to specificexamples and embodiments, not to be constructed as limiting the scope ofthis invention in any way. It is understood that various modificationsand additions can be made to the specific examples and embodimentsdisclosed without departing from the spirit of the invention, and suchmodifications and additions are contemplated as being part of thepresent invention.

1. A curing agent comprising a compound of Formula I or a salt thereof:

wherein n is an integer greater than 1; A is alkylene,alkylene-hetero-alkylene, alkenylene, alkenylene-hetero-alkenylene,alkylene-hetero-alkenylene, alkynylene, cycloalkylene,alkylene-cycloalkylene, alkylene-cycloalkylene-alkylene,alkenylene-cycloalkylene, alkenylene-cycloalkylene-alkenylen,alkylene-cycloalkylene-alkenylene, alkynylene-cycloalkylene,alkynylene-cycloalkylene-alkynylene, heterocycloalkylene,alkylene-heterocycloalkylene, alkylene-heterocycloalkylene-alkylene,alkenylene-heterocycloalkylene,alkenylene-heterocycloalkylene-alkenylene,alkylene-heterocycloalkylene-alkenylene, alkynylene-heterocycloalkylene,alkynylene-heterocycloalkylene-alkynylene, cycloalkenylene,alkylene-cycloalkenylene, alkylene-cycloalkenylene-alkylene,alkenylene-cycloalkenylene, alkenylene-cycloalkenylene-alkenylene,alkylene-cycloalkenylene-alkenylene, alkynylene-cycloalkenylene,alkynylene-cycloalkenylene-alkynylene, heterocycloalkenylene,alkylene-heterocycloalkenylene, alkylene-heterocycloalkenylene-alkylene,alkenylene-heterocycloalkenylene,alkenylene-heterocycloalkenylene-alkenylene,alkylene-heterocycloalkenylene-alkenylene,alkynylene-heterocycloalkenylene,alkynylene-heterocycloalkenylene-alkynylene, arylene, arylene-X-arylene,alkylene-arylene, alkylene-arylene-alkylene, alkenylene-arylene,alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene,alkynylene-arylene, alkynylene-arylene-alkynylene, heteroarylene,heteroarylene-X-heteroarylene, heteroarylene-X-arylene,alkylene-heteroarylene, alkylene-heteroarylene-alkylene,alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene,alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, oralkynylene-heteroarylene-alkynylene; X is alkylene, alkenylene, oxygen,sulfur, nitrogen, sulfoxide, sulfone, carbonyl, —C(O)O—, —OC(O)O—,—OC(O)NH—, —C(O)NH—, or —HNC(O)NH—; each B independently is hydrogen,alkyl, cycloalkyl, heterocyclic, heterocycloalkyl, alkenyl,cycloalkenyl, aryl, arylalkyl, heteroaryl, heteroarylalkyl,alkyl-hetero-alkyl, alkyl-hetero-alkenyl, or alkynyl; or, A and at leastone B, together with the carbon atom to which they are bonded, form asaturated or unsaturated ring optionally containing at least one heteroring atom of O, S, N, or P; or, at least two B groups, together with Aand carbon atoms to which A and B groups are bonded, form a saturated orunsaturated ring optionally containing at least one hetero ring atom ofO, S, N, or P.
 2. The curing agent of claim 1, wherein n is 2, 3, or 4.3. The curing agent of claim 2, wherein n is
 2. 4. The curing agent ofclaim 1, wherein A is alkylene, alkylene-hetero-alkylene, alkenylene,alkenylene-hetero-alkenylene, alkylene-hetero-alkenylene, cycloalkylene,heterocycloalkylene, arylene, arylene-X-arylene, alkylene-arylene,alkylene-arylene-alkylene, alkenylene-arylene,alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene,alkynylene-arylene, alkynylene-arylene-alkynylene, heteroarylene,heteroarylene-X-heteroarylene, heteroarylene-X-arylene,alkylene-heteroarylene, alkylene-heteroarylene-alkylene,alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene,alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, oralkynylene-heteroarylene-alkynylene.
 5. The curing agent of claim 4,wherein A is alkylene, arylene, heteroarylene, arylene-X-arylene,heteroarylene-X-heteroarylene, or heteroarylene-X-arylene.
 6. The curingagent of claim 5, wherein A is alkylene, arylene, or arylene-X-arylene.7. The curing agent of claim 6, wherein A is methylene, ethylene,propylene, phenylene, or phenylene-X-phenylene.
 8. The curing agent ofclaim 1, wherein X is alkylene, oxygen, sulfur, nitrogen, sulfoxide,sulfone, or —OC(O)O—.
 9. The curing agent of claim 8, wherein X isoxygen, sulfur, nitrogen, sulfoxide, or sulfone.
 10. The curing agent ofclaim 1, wherein each B independently is hydrogen, alkyl,alkyl-hetero-alkyl, alkenyl, alkenyl-hetero-alkenyl,alkenyl-hetero-alkyl, alkyl-hetero-alkenyl, or alkynyl.
 11. The curingagent of claim 10, wherein each B independently is hydrogen or alkyl.12. The curing agent of claim 1, wherein the compound of Formula I is:


13. The curing agent of claim 1, wherein A and at least one B, togetherwith the carbon atom to which they are bonded, form a 3- to 8-memberedsaturated or unsaturated ring optionally containing at least one heteroring atom.
 14. (canceled)
 15. (canceled)
 16. (canceled)
 17. (canceled)18. (canceled)
 19. (canceled)
 20. (canceled)
 21. (canceled)
 22. Adegradable cross-linked polymer comprising a cleavable cross-linkinggroup derived from a curing agent of claim 1 and an epoxy resin, whereinat least one amino group in the curing agent is fully reacted to loseboth hydrogen atoms and form two bonds with the epoxy resin.
 23. Thedegradable cross-linked polymer of claim 22, wherein the epoxy resincomprises a glycidyl ether epoxy resin, glycidyl ester epoxy resin,glycidyl epoxy amine epoxy resin, trifunctional epoxy resin,tetrafunctional epoxy resin, novolac epoxy resin, o-cresol formaldehydeepoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, ornitrogen-containing epoxy resin.
 24. The degradable cross-linked polymerof claim 22, wherein the cleavable cross-linking group is derived from

and at least one amino group of which is fully reacted to lose bothhydrogen atoms.
 25. A recyclable prepreg composition or reinforcedcomposite material, comprising a curing agent of claim 1, an epoxyresin, an auxiliary material, and a reinforcing material, wherein: theepoxy resin comprises glycidyl ether epoxy resin, glycidyl ester epoxyresin, glycidyl epoxy amine epoxy resin, trifunctional epoxy resin,tetrafunctional epoxy resin, novolac epoxy resin, o-cresol formaldehydeepoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, ornitrogen-containing epoxy resin; the reinforcing material comprisescarbon nanotube, boron nitride nanotube, carbon black, metalnano-particle, metal oxide nanoparticle, organic nanoparticle, ironoxide, glass fiber, carbon fiber, natural fiber, synthetic fiber, orfabrics made therefrom; and the auxiliary material comprisesaccelerator, diluent, plasticizer, toughening agent, thickening agent,coupling agent, defoamer, flatting agent, ultraviolet absorber,antioxidant, brightener, fluorescent agent, pigment, or filler.
 26. Amethod for degrading a degradable cross-linked polymer of claim 24 or arecyclable prepreg composition or reinforced composite material of claim25, comprising the steps of: (1) under the heating and stirringconditions, immersing the polymer in a mixed acid and solvent system toobtain a degradation solution; and (2) using an alkaline solution tocontrol the pH of the degradation solution.
 27. The method of claim 26,further comprising a step of washing and drying the precipitate anddegradation solution after pH adjustment in step (2).
 28. The method ofclaim 26, wherein the acid comprises a hydrochloric acid, hydrobromicacid, hydrofluoric acid, acetic acid, trifluoroacetic acid, lactic acid,formic acid, propionic acid, citric acid, methanesulfonic acid,p-toluenesulfonic acid, nitric acid, sulfuric acid, sulfurous acid,phosphoric acid, perchloric acid, benzoic acid, salicylic acid, orphthalic acid; the alkali comprises lithium hydroxide, sodium hydroxide,potassium hydroxide, calcium hydroxide, sodium carbonate, sodiumbicarbonate, potassium carbonate, potassium bicarbonate, or ammonia;each of the solvent for immersing the polymer in step (1) and thesolvent for the alkaline solution in step (2) independently comprisesmethanol, ethanol, ethylene glycol, propanol, isopropanol, butanol,isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol,benzyl alcohol, phenethyl alcohol, p-hydroxymethyl benzene,m-hydroxymethyl benzene, o-hydroxy benzene, p-hydroxyethyl benzene,m-hydroxyethyl benzene, o-hydroxyethyl benzene, water,N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone,dimethyl sulfoxide, tetrahydrofuran, methyl tetrahydrofuran, glycerol,or dioxane.
 29. The method of claim 26, wherein in step (1), the heatingtemperature is in the range of 80˜150° C., and the heating time is 4˜8hours, and the mass concentration of the acid in the solvent system is0.5˜20% (w/w); and in step (2), the temperature is in the range of 5˜50°C., the final pH is 6˜12, and the mass concentration of the alkali inthe solvent is 5˜30% (w/w).
 30. A method for preparing a curing agent ofclaim 1, comprising reacting a compound of Formula I-a with hydrazine,wherein A and B in Formula I-a are the same as defined in claim
 1.


31. (canceled)
 32. The method of claim 30, wherein the mole ratio of thecompound of Formula I-a or the compound of Formula II-a to hydrazine is1:2˜100, and the reaction is conducted at a temperature of −20˜150° C.